The Efficiency of Sclerotherapy for the Management of Endometrioma: A Systematic Review and Meta-Analysis of Clinical and Fertility Outcomes

Background and Objectives: The most common sites of implantation of endometriotic tissue are the ovaries. Endometriomas are present in most cases of endometriosis (up to 45%). Although laparoscopic cystectomy is the standard of care in endometrioma, new strategies have been set up to minimize iatrogenic injuries to ovarian tissue. Sclerotherapy consists of injecting alcohol into the endometrioma to denature the amino acidic components of its pseudocapsule. The aim of this systematic review and meta-analysis is to compare clinical and pregnancy outcomes in surgery and sclerotherapy. Materials and Methods: Following the recommendations in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement, we systematically searched PubMed, EMBASE, Scopus, Google Scholar, Clinical-trials.gov, and the Cochrane Central Register of Controlled Trials databases in January 2023, adopting the string “Endometriosis and sclerotherapy”. We made no limitations on the country and year of publication. We included the studies containing Success Rate (SR), Recurrence Rate (RR), Pregnancy Rate (PR) before and after the procedure. We used comparative studies for meta-analysis. Results: A total of 29 studies fulfilled inclusion criteria, 7 retrospective observational studies and 22 prospective studies. Eight comparative studies were enrolled in meta-analysis. Patients were analyzed concerning the number of recurrences and pregnancies in surgery, and compared with sclerotherapy. Four studies showed SR > 80.0%, and only two had SR < 80.0%, of which one consisted of tetracycline instillation. Only 1 study had 100% PR, the other 14 reported PR > 30.0%, whereas six had PR < 30.0%, of which one showed 0.0% PR with ethanol injection at two-thirds of the cyst fluid volume. Meta-analysis highlighted a non-significant lower incidence of recurrence in the surgery group compared to the sclerotherapy group (p = 0.87). In parallel, the surgery group showed a non-significant better PR than the sclerotherapy group (p = 0.08). Conclusions: Despite sclerotherapy having a minor incidence of postoperative complications compared to surgery, the latter is associated with a lower RR and better PR. However, those data assert the importance of a targeted therapy according to preoperative conditions and reproductive potential.


Introduction
Endometriosis is an estrogen-dependent gynecological disorder affecting 10% of childbearing-age women [1].It consists of the migration of endometrial tissue (stroma plus glands) outside the uterine cavity.The most common sites of implantation are the ovaries, which could result in a superficial or deep variant [1].In particular, the deep form of ovarian endometriosis is represented by endometrioma-an ovarian cyst encapsulated by endometrial tissue and containing dark brown fluid, deriving from blood catabolism [2].Endometriomas are present in almost 45% of cases of endometriosis [2].Nowadays, the standard of care in endometrioma is laparoscopic cystectomy [3].Given the chronic nature of endometriosis, the treatment strategy could be repeated; however, surgery damages residual ovarian parenchyma.The damage may result in a reduction in the patient's fertile potential, with a risk of infertility and early menopause.For this reason, iatrogenic damage should be minimized, and a strategy should be devised to resolve the clinical episode with the least possible sequelae.The surgical instruments and coagulation for hemostasis could damage the ovarian tissue [4][5][6].So, various research groups have studied alternative strategies for treating endometrioma.One of the most popular is the use of sclerotherapy.The rationale for sclerotherapy is to destroy the pseudocapsule of the endometrioma by instilling alcoholic substances inside it [7].Sclerotherapy has been considered a costeffective and safe option to preserve healthy ovarian tissue with a low incidence of Clavien-Dindo complications [8][9][10][11][12].The practitioner should perform an injection of a sclerosing substance into the cyst, to proceed with washing or retention [13].Hydrosoluble dehydrating antiseptic fluids are able to denature the proteins upon the envelop of microorganisms and dissolve their capsule's lipids.In most cases, the ethanol is preferred to sclerosing substances because it has shown better outcomes in the management of renal and hepatic cysts [7].Sclerotherapy can be practiced through the use of both general or local anesthetics, and it is well-tolerated by the patients.The feasibility in programming, cost-effectiveness, and rapid recovery after the technique suggest that it can be considered the standard of care for minimally invasive interventions, like ethanol sclerotherapy of ovarian endometrioma [7].Nevertheless, to date, no randomized clinical trials have proven the greater effectiveness of one technique over the other, either in terms of reducing the recurrence rate or improving pregnancy rates.The aim of the present systematic review and meta-analysis was to evaluate clinical and pregnancy outcomes of sclerotherapy in managing ovarian endometriomas, compared to standard cystectomy.

Materials and Methods
The present study was exempted from ethical approval, because it does not include interventions on human subjects.The methods for this study were specified a priori based on the recommendations in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [14].The review is registered on PROSPERO as ID394764.

Search Method
We performed systematic research for records about the use of sclerotherapy in managing ovarian endometriomas in PubMed, EMBASE, Scopus, Google Scholar, Clinicaltrials.gov,and the Cochrane Central Register of Controlled Trials in January 2023.We made no restriction on country, nor year of publication, and considered only entirely English published studies.We adopted the following string of idioms in each database to identify studies fitting to our review's topic: "Endometriosis and sclerotherapy".

Study Selection
Study selection was made independently by I.I. and M.G.V.In case of discrepancy, C.R. decided on inclusion or exclusion.Inclusion criteria were: (1) studies that included patients with at least one ovarian endometrioma, treated with sclerotherapy and/or surgery; (2) studies reporting at least one outcome of interest: Success Rate (SR), Recurrence Rate (RR); Pregnancy Rate (PR) after the procedure (3) peer-reviewed articles, published originally.We excluded: non-original studies, pre-clinical trials, animal trials, abstract-only publications, and articles in a language other than English.If possible, the authors of studies that were published as conference abstracts were tried to be contacted via e-mail and asked to provide their data.We mentioned the studies selected and all reasons for exclusion in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart (Figure 1).We assessed all included studies concerning potential conflicts of interest.
Medicina 2023, 59, x FOR PEER REVIEW 3 of 17 exclusion in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart (Figure 1).We assessed all included studies concerning potential conflicts of interest.

Statistical Analysis
Heterogeneity among comparative studies was tested using the Chi-square test and I-square tests [15].Risk rates and 95% confidence intervals (CI) were used for dichotomous variables.Fixed-effect models conducted statistical analysis without significant heterogeneity (I2 < 50%), or models if I2 > 50%.SR, RR, complications rate, and PR were the clinical outcomes.SR (number of healed patients among the number of attempts with sclerotherapy or surgery), RR (the number of relapses during follow-up), and PR (number of pregnant patients over the total of women who tried to conceive) were calculated in each study as percentages.The chi-square test was used to compare continuous variables.

Quality Assessment
We assessed the quality of included studies using the Newcastle-Ottawa Scale (NOS) [16].That assessment scale uses three broad factors (selection, comparability, exposure), with scores ranging from 0 (lowest quality) to 9 (best quality).Two Authors (C.R. and I.I.) independently rated the studies quality.Any disagreement was subsequently resolved by discussion or consultation with P.F.G.We reported NOS Scale in Appendix A. We used a funnel plot analysis to establish publication bias.We employed Egger s regression test to determine the asymmetry of the funnel plots (Appendices B and C).

Statistical Analysis
Heterogeneity among comparative studies was tested using the Chi-square test and I-square tests [15].Risk rates and 95% confidence intervals (CI) were used for dichotomous variables.Fixed-effect models conducted statistical analysis without significant heterogeneity (I2 < 50%), or models if I2 > 50%.SR, RR, complications rate, and PR were the clinical outcomes.SR (number of healed patients among the number of attempts with sclerotherapy or surgery), RR (the number of relapses during follow-up), and PR (number of pregnant patients over the total of women who tried to conceive) were calculated in each study as percentages.The chi-square test was used to compare continuous variables.

Quality Assessment
We assessed the quality of included studies using the Newcastle-Ottawa Scale (NOS) [16].That assessment scale uses three broad factors (selection, comparability, exposure), with scores ranging from 0 (lowest quality) to 9 (best quality).Two Authors (C.R. and I.I.) independently rated the studies' quality.Any disagreement was subsequently resolved by discussion or consultation with P.F.G.We reported NOS Scale in Appendix A. We used a funnel plot analysis to establish publication bias.We employed Egger's regression test to determine the asymmetry of the funnel plots (Appendices B and C).

Studies' Characteristics
After the database search, 134 articles matched the searching criteria.After removing records with no full-text, duplicates, and wrong study designs (e.g., reviews), 37 were suitable for eligibility.Of those, 29 matched inclusion criteria and were included in the systematic review.A total of 21 of them were non-comparative, single-armed studies evaluating only sclerotherapy .The other eight studies were comparative studies between surgery and sclerotherapy and were included in quantitative analysis (Figure 1) [37][38][39][40][41][42][43][44][45].The countries where the studies were conducted, the publication year range, the studies' design, number of participants, substance instilled, and procedure characteristics are summarized in Table 1.The quality of all studies was assessed by NOS [16] (Appendix A).Overall, the publication years ranged from 1997 to 2022 .In total, 1642 patients with endometriomas were included .The follow-up (FU) period ranged from 1.5 to 84 months on average .

Meta-Analysis
The eight studies comparing surgery and sclerotherapy were enrolled in the metaanalysis, exploring outcomes about recurrence and pregnancy.Four studies reported data about recurrences events.A total of 303 patients were analyzed, 148 in the surgery arm and 155 in the sclerotherapy arm.A total of 17 recurrences occurred in the surgery group vs. 27 recurrences in the sclerotherapy group.Because of the high heterogeneity (I262%; p = 0.05), a random-effects model was applied.
The surgery group showed a comparable incidence of recurrence than the sclerotherapy group (OR 0.87 [95% CI 0.18-4.32]p = 0.87) (Figure 2).tive studies reported useful data.There was a total of 204 patients for the surgical group and 166 for the sclerotherapy group.Only patients attempting to become pregnant were considered in the second analysis.A total of 370 patients were analyzed, 204 in the surgery arm and 166 in the sclerotherapy arm.A total of 67 pregnancies occurred in the surgery group, vs. 72 recurrences in the sclerotherapy group.Because of the high heterogeneity (I260%; p = 0.02), a random-effects model was applied.
In addition, in that analysis, the surgical group documented a comparable pregnancy rate than the sclerotherapy (OR 0.47 [95% CI 0.21-1.09]p = 0.08) (Figure 3).We performed a second analysis of the pregnancy rate.Seven of the eight comparative studies reported useful data.There was a total of 204 patients for the surgical group and 166 for the sclerotherapy group.Only patients attempting to become pregnant were considered in the second analysis.A total of 370 patients were analyzed, 204 in the surgery arm and 166 in the sclerotherapy arm.A total of 67 pregnancies occurred in the surgery group, vs. 72 recurrences in the sclerotherapy group.Because of the high heterogeneity (I260%; p = 0.02), a random-effects model was applied.

Discussion
Sclerotherapy is a method that is finding increasing acceptance in treating endometriomas.The reported data show that the SR is high when this technique is applied.In our opinion, the real comparison between the surgical technique and sclerotherapy should be made on the one hand on the RR, to optimize the chronification of the pathology and minimize treatment event, and, on the other hand, on the PR, to have an indirect view of how the treatment may have iatrogenic damage.The data reported in this systematic review show that sclerotherapy in endometriomas has a varied RR, ranging from 0.0% to 61.9%.However, except for a few studies, most literature data report recurrence rates <30%, over an average FU period of 1 year.However, the meta-analysis reported, even without statistical significance, a minor incidence of recurrence in the surgery arm compared to the sclerotherapy group (Figure 2).In parallel, despite the fact that PR reaches up to 100% in the sclerotherapy group, the surgery arm revealed better PR.Differences in scientific evidence in terms of RR and PR may be due to the methodology employed-in particular, sclerosing substance, but also concentration, instilled proportions, and duration of retention.The sclerosing agent seems to be relevant since sclerotherapy with tetracyclines or methotrexate had higher RR and lower PR.Tetracyclines and methotrexate act in the cell-cycle functions through molecular pathways, whereas ethanol injuries endometrioma s pseudocapsule with a mechanism including cytotoxicity, thrombosis, and cells hypertonic dehydration [21,46,47].Apparently, long ethanol retention times and small dilutions may be associated with the complete degradation of the pseudocapsule s cytoarchitecture.However, due to the heterogeneity of data among studies, it was impossible to assess the ideal ethanol retention times or dilution percentages.Only one study, Noma et al. in 2001, reported a difference in RR deeply in favor of sclerotherapy beside the laparoscopic cystectomy (up to 97.6% vs. 67.0%-p< 0.05); however, the sample size was exigu-

Discussion
Sclerotherapy is a method that is finding increasing acceptance in treating endometriomas.The reported data show that the SR is high when this technique is applied.In our opinion, the real comparison between the surgical technique and sclerotherapy should be made on the one hand on the RR, to optimize the chronification of the pathology and minimize treatment event, and, on the other hand, on the PR, to have an indirect view of how the treatment may have iatrogenic damage.The data reported in this systematic review show that sclerotherapy in endometriomas has a varied RR, ranging from 0.0% to 61.9%.However, except for a few studies, most literature data report recurrence rates <30%, over an average FU period of 1 year.However, the meta-analysis reported, even without statistical significance, a minor incidence of recurrence in the surgery arm compared to the sclerotherapy group (Figure 2).In parallel, despite the fact that PR reaches up to 100% in the sclerotherapy group, the surgery arm revealed better PR.Differences in scientific evidence in terms of RR and PR may be due to the methodology employed-in particular, sclerosing substance, but also concentration, instilled proportions, and duration of retention.The sclerosing agent seems to be relevant since sclerotherapy with tetracyclines or methotrexate had higher RR and lower PR.Tetracyclines and methotrexate act in the cell-cycle functions through molecular pathways, whereas ethanol injuries endometrioma's pseudocapsule with a mechanism including cytotoxicity, thrombosis, and cells hypertonic Medicina 2023, 59, 1643 9 of 16 dehydration [21,46,47].Apparently, long ethanol retention times and small dilutions may be associated with the complete degradation of the pseudocapsule's cytoarchitecture.However, due to the heterogeneity of data among studies, it was impossible to assess the ideal ethanol retention times or dilution percentages.Only one study, Noma et al. in 2001, reported a difference in RR deeply in favor of sclerotherapy beside the laparoscopic cystectomy (up to 97.6% vs. 67.0%-p< 0.05); however, the sample size was exiguous, and the study design was retrospective, including the years in which laparoscopic treatment was growing up [38].In Appendix B, it is demonstrated, however, that results are homogeneous in the scientific literature, regarding the outcomes of recurrence.Regarding pregnancy outcomes, it must be considered that women with endometriomas have themselves lower ovarian reserve, perhaps due to a decreased response in Assisted-Reproductive Technology (ART) techniques [48].However, surgical interventions themselves impact ovarian tissue and antral follicle count, revealed by modifications of Anti-Müllerian Hormone (AMH) [49][50][51][52].In addition, repeated surgeries can also lead to adhesion syndrome, resulting in worsened fertility.Ethyl alcohol instillation can also damage follicles; however, the significant heterogeneity of studies makes it complicated to identify a dose and administration time that maximizes the result while minimizing the ovariotoxic effect.Our data analysis highlighted that there is homogeneity between the considered studies.It is shown through the Pregnancy Funnel Plot in Appendix C. It would be appropriate to understand whether adjuvant treatment options after sclerotherapy could improve PR and ameliorate ART response rates-for example, an increased dose of gonadotropins in women with preserved ovarian reserve.A further point to be made is about patient selection.In fact, sclerotherapy might be an alternative in cases of single endometriomas.In contrast, the endometrioma itself might be multiple or associated with pictures of severe endometriosis, where surgical approaches remain essential [53].
The main limitation of our systematic review and meta-analysis is the small number of randomized trials comparing sclerotherapy to surgery.Moreover, some articles included a poor number of patients, and heterogeneity among procedures could increase risks of bias and confounding.In addition, the term sclerotherapy embraces a range of methods that differ in substance and mode of administration, which is why our data are difficult to put into context.In any case, our results show a novelty in the landscape of current knowledge assessing lower RR and better PR in sclerotherapy compared to surgery [13].Moreover, we highlight that sclerotherapy has a minimal incidence of Clavien-Dindo complications, and neither study showed Clavien-Dindo 3 or more sequelae after ethanol injection.Although, the overall complication amount in laparoscopy is low, and it is only constituted by intraoperative complexity due to previous surgeries [54].
Otherwise, since the presence of ovarian endometriomas is often associated with deep endometriosis, symptoms like chronic pelvic pain may be related mostly to deep adhesions [55].Hence, amelioration of symptoms in women with ovarian endometrioma even after sclerotherapy could be improper.This could be considered as a further point of weakness of our study, and it would be feasible to investigate upon the detection of markers of deep infiltrating endometriosis [56,57].Due to the comparable clinical and pregnancy outcomes of laparoscopic cystectomy and sclerotherapy in patients with endometriomas, the latter could be considered the standard of care in women with no evidence of deep endometriosis, given the cost-effectiveness and patient comfort of sclerotherapy.Unfortunately, there are poor data about the use of alcohol injection in young women with the desire of pregnancy.Although, according to recent evidence, ethanol injection shows better reproductive outcomes in women undergoing Assisted Reproductive technology [34,45,58,59].Sclerotherapy may be a factual option also when a deeper surgery is contraindicated or in women with ovarian tissue injury or at risk of iatrogenic damage.Further perspectives may focus on the use of liquid biopsy or microbial composition to identify the best candidates for sclerotherapy [60,61].Regarding the former, the detection of micro-RNAs (miRNAs)-a class of small RNA molecules, composed of 15-22 nucleotides each-may be associated with particular features of the endometrioma [60].Regarding the latter, intestinal or Female Reproductive Tract (FRT) microbiota may be linked to fertility outcomes [61].Those findings would be helpful in tailoring the management of patients with ovarian endometriomas, using molecular strategies in order to identify key characteristics to plan the best treatment modality.

Conclusions
Although sclerotherapy shows a low rate of complications in the postoperative period, surgery seems to be associated with decreased RR and higher PR.Our analysis demonstrates comparable incidence of recurrence and pregnancy rate between surgery and sclerotherapy, with homogeneity between the findings (Sections B and C).Those data highlight the importance of a targeted therapy according to preoperative conditions and reproductive potential based on ovarian reserve in endometriosis-affected patients.Otherwise, sclerotherapy could be a safe and valid alternative in patients contraindicated for more complex surgery.Further evidence is needed to optimize and standardize the amount and duration of ethanol injection.

Appendix A
Newcastle-Ottawa Scale.

Figure 1 .
Figure 1.PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) Flow-Diagram.

Figure 1 .
Figure 1.PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) Flow-Diagram.

Table 1 .
Characteristics of studies included.

Table 2 .
Clinical outcomes after sclerotherapy of ovarian endometrioma.

Table 3 .
Reproductive outcomes after sclerotherapy of ovarian endometrioma.

Author, Year of Publication Country Study Design Selection Comparability Exposure Tot.
Medicina 2023, 59, x FOR PEER REVIEW 14 of 17Appendix CPregnancy Funnel Plot.